The invention relates to the control of the rotation speed of an electric motor of a motor vehicle, and more particularly the reduction of the oscillations of the rotation speed.
Control of the rotation speed of an electric motor generally makes it possible to interpret the will of the driver who acts on the accelerator and brake pedals to generate a positive or negative torque setpoint. This torque setpoint is transmitted to the power electronic components (chopper, inverter, etc) to generate electrical setpoints (current and voltage) to obtain the desired torque and finally a rotation speed of the motor.
Generally, “drive train” is used to refer to all the electromechanical members which ensure the transmission of a torque setpoint to the wheels (power electronics, electric motor, engine suspension, reducing gear, etc.).
Conventionally, to follow a torque setpoint changing from 0 to a positive value, the rotation speed of the motor will increase to a value corresponding to the desired torque. That said, this increase is generally not linear (ideal response) and oscillations occur.
When running normally, the torque setpoint undergoes variations. These variations are generally not perfectly followed by the speed of the motor and damped oscillations can be observed in the trend of the rotation speed of the motor. These oscillations are disagreeable to the driver of the vehicle.
Also, with the electric machines being capable of producing very strong torque levels within very short delays, the phenomenon described above is amplified by comparison to the drive trains provided with heat engines.
It has been proposed to reduce the oscillations by correcting the torque setpoint on the basis of a measurement of the engine speed (or of the speed of the vehicle). More specifically, it has been proposed to twice derive the engine speed to extract therefrom only the annoying oscillations, and to multiply the twice-derived engine speed by a coefficient in order to finally subtract the result from a torque setpoint.
This solution is suited to oscillations occurring in vehicles with heat engines. This solution is not fast enough to deal with the oscillations in a vehicle with electric or hybrid drive. Also, this solution has the drawback of being delayed relative to the oscillations that it cannot anticipate.
Reference will also be able to be made to the document WO 2012/011521 which proposes using a direct corrector and a feedback-based corrector. The direct corrector of this document filters the variations of the torque setpoint in order to avoid excessively exciting the frequencies in the resonance area of the drive train. The feedback-based corrector reduces the oscillations by modifying the gain and the phase of the frequency response of the drive train in the resonance area.
FIG. 1 shows a schematic representation of the association of the direct corrector and of the feedback-based corrector of the document WO 2012/011521. A torque setpoint Ccons is first of all generated, for example from information supplied by the pedals of the vehicle and corresponds to the torque setpoint as desired by the driver. This setpoint Ccons is applied to the input of a direct corrector 1 having the following transfer function:
            G      obj        ⁡          (      s      )                  G      ^        ⁡          (      s      )      
With:
Gobj(s) being the objective transfer function, that is to say without oscillations,
Ĝ(s) being the control model, that is to say the model of the drive train.
An adder 2 is linked by a first input to the output of the corrector 1. The output of the adder 2 is linked to a first input of another adder 3, another input of which receives a disturbance Cperturb. The output of the adder 3 communicates with the drive train 4 which has a transfer function G(s). The drive train 4 makes it possible to obtain a rotation speed of the motor ωmot.
The feedback-based corrector described in this document comprises a corrector 5 having the transfer function Ĝ(s) whose output is compared with the speed of the motor ωmot (subtractor 6). The output of the subtractor 6 is linked to an additional corrector 7 having the transfer function:
      H    ⁡          (      s      )                  G      ^        ⁡          (      s      )      
In which H(s) is chosen to correct the oscillations.
The control model Ĝ(s) has a frequency response revealing a resonance area accompanied by a phase shift. Furthermore, this control model is incomplete and does not precisely correspond to the real drive train, although it is intended to operate if the following relationship is verified:{circumflex over (G)}(s)=G(s)
This relationship does not make it possible to take into account the ageing of the drive trains and the dispersion of their properties over a number of vehicles.